[Dovecot] Question about "slow" storage but fast cpus, plenty of ram and dovecot

Mon Dec 13 11:26:15 EET 2010

El 13/12/10 10:16, Brad Davidson escribió:
>
> On Dec 12, 2010, at 23:26, Javier de Miguel Rodrí guez<javierdemiguel at us.es>  wrote:
>
>>     My SAN(s) (HP LeftHand Networks) do not support SSD, though. But I have several LeftHand nodes, some of them with raid5, others with raid 1+0. Maildirs+indexes are now in raid5, maybe I can separate the indexes to raid 1+0 iscsi target in a different san
>>
>>     I have two raid5 (7 disks+1 spare) and I have joined them via LVM stripping. Each disk is SAS 15k rpm 450GB, and the SANs have 512 MB-battery-backed-cache. In our real workload (imapsync), each raid5 gives around 1700-1800 IOPS, combined 3.500 IOPS.
> Your 'slow' storage is running against 16 15k RPM SAS drives? Those LeftHand controllers must be terrible. We have Maildir on NFS on a Netapp with 15k RPM 450GB FC disks and have never had performance problems, even when running the controllers up against the wall by mounting with the noac option (60k NFS IOPS!). We were using 500GB 4500 RPM ATA disks at that point - doesn't get much slower than that.

     Can you give me (off-list if you desire) more info about your 
setup? I am interested in the number and type of spindles you are using. 
We are using LeftHand because of their real time replication 
capabilities, something very interesting to us, and each node pair is 
relatively cheap (8x450 GB at 15K rpm sas disks per node, real time 
replication, 512 MB caché, about 25K € each node pair).

     We can throw more hardware to this, let's see if using memory-based 
indexes (via ramdisk) we get better results. Zlib compression on indexes 
should be great for this.

     Regards

     Javier